In conventional cellular and PCS (Personal Communications System) wireless systems, signals transmitted from a base station (cell site) to a user (remote terminal) are usually received via an omnidirectional antenna; often in the form of a stub antenna. Such systems often sacrifice bandwidth to obtain better area coverage, stemming from the result of less-than-desirable signal popagation characteristics. For instance, the bit binary digit-to-Hz ration of the typical digital cellular or PCS system is often less than 0.5. Lower binary signal modulation types, such as BPSK (Binary Phase Shift Keying) are used, since the effective SNR (Signal to Noise Ratio) or C/I (Carrier to Interference Ratio) are often as low as 20 dB. In fact, for voice-based signaling, the threshold C/I (or SNR) ratio (SNR) for adequate quality reception of the signal is about 17 dB. Conventional omnidirectional antennas do not provide either enough bandwidth or enough gain for applications involving broadband services, such as Internet data and the like. In order to achieve more gain, with the goal being at least 6 dBi (isotropic) some other alternative is necessary. In this regard, some providers require from as much as 10 to 20 dBi directional gain for customer equipment.
Data applications require higher C/I characteristics. For example, for wireless systems directed toward data applications, it is desirable to significantly increase the SNR or C/I in order to employ higher order modulation techniques, such as a QAM-64 (Quadrature Amplitude Modulation, with 64 points in the complex constellation). These higher order modulation schemes require substantially greater C/I (or SNR) thresholds; typically higher than 26 dB. For the case of MMDS (Multichannel Multipoint Distribution System) signals, where the carrier frequencies are higher (around 2500 MHz), the propagation characteristics are even worse. There is a need, therefore, for transmission systems that can both satisfy the coverage (progagation) demands, as well as generate high C/I or SNR levels, such as for data applications.
One option for improving C/I characteristics is to increase the terminal equipment (TE), or remote, antenna gain. This requires increasing the physical size of the antenna. Additionally, it helps to increase the elevation (i.e., vertical height above ground level) of the antenna, if that is an available option.
For example, in conventional analog MMDS systems, an increase of SNR or C/I has been traditionally accomplished by installing a large reflector type antenna or flat plate array (with up to 30 dBi of directional gain) on a rooftop, or a pole. The disadvantages of such a solution include a complex, difficult, and costly installation, as well as poor aesthetics. The migration of the MMDS frequency spectrum, however, from an analog video system to a wireless data and Internet system, demands a less complex and more user friendly antenna installation method. It also demands a much lower cost. The difficulty in such a solution is in designing a system with sufficient directional gain to overcome losses in transmission through walls, and which is also easy to install and orient without requiring specialized skills by the consumer or others.
Simultaneously, in wireless communications using cellular phones or other consumer-based, Customer Premises Equipment (CPE), there is also a need for similar types of antennas and systems. More specifically, CPE antenna systems with directional characteristics or beamsteering for added gain and C/I improvement are desirable. An omnidirectional mode of operation is also still desirable, as well. For example, it may be desirable to scan omnidirectionally for other incoming signals while simultaneously receiving/transmitting a given signal from/to a given direction with increased gain provided by beamsteering or a beam shaping of an antenna to the direction of the incoming/outgoing signal.
Accordingly, it is desirable to have an antenna system which provides desirable C/I characteristics, such as for wireless data systems.
Simultaneously, it is also desirable to maintain omnidirectional characteristics for good area coverage.
The present invention addresses these and other needs in the art as discussed below in greater detail.
The above-mentioned omnidirectional and beam steering antenna, which is more fully described hereinbelow, provides a simple and inexpensive solution to the above-discussed problems.